Effect of Face Losses and Cover-to-Diameter Ratio on Tunneling Induced Settlements in Soft Clay, Using Transparent Soil Models

Reliable prediction of surface and subsurface settlements induced by shallow tunnels is important to minimize the adverse effects which may take place during tunnel excavation. A transparent soil surrogate representing the geotechnical behavior of soft clay was employed to explore spatial soil deformations within the soil mass near the tunnel. Shear strain, volumetric strain, surface and subsurface settlements resulting from increasing face losses were captured for three cover-to-diameter (C/D) ratios. The observed data trends are generally consistent with the data available in the literature, however the ability to visualize soil movements confirmed a number of perceived behaviors. First, the observed subsurface settlements are noticeably larger than surface ones. Second, the observed settlement trough widths are generally wider than the predicted ones, consistent with the low shear strength of the clay simulant. Third, calculated volumetric strains demonstrated the formation of an arching zone. Arching action slowly dissipates at higher C/D ratio, which may impact tunnel crown stability.